In a heat exchanger employing U-flow evaporator tubes, the refrigerant changes from a liquid to a gaseous phase as it flows from the inlet side to the outlet side of each tube. However, as the refrigerant flows around the bottom, or top corners, depending on evaporator orientation, the flow stays closer to the inside and near the separating rib. This causes liquid refrigerant starvation with only vapor present in the corners of the tubes which accordingly have low heat conversion capacity. This can be readily observed in thermographs as hot spots in an evaporator which are detrimental to heat transfer performance of the evaporator.
In the heat exchangers disclosed in my copending application, U.S. Ser. No. 677,193, filed Mar. 29, 1991, for HIGH EFFICIENCY HEAT EXCHANGER WITH DIVIDER RIB LEAK PATHS, now U.S. Pat. No. 5,062,477, issued Nov. 5, 1991, assigned to the assignee of this invention and hereby incorporated by reference, construction is provided to improve heat exchanger performance by minimizing dry out areas. More particularly, in my copending application, spaced leak paths are formed in the centralized divider rib of U-flow type tubes of an evaporator for an air conditioner system to ensure that some of the liquid refrigerant would be short circuited from the inlet to the outlet or vapor side of the tube so that localized dry out and hot spots would be reduced or eliminated and heat exchanger efficiency would be thereby improved.
The heat exchanger of this invention is of the general category of that disclosed in my copending application, and has a plurality of flattened tubes which are operatively joined at their upper tank ends to form a core for the passage of volatile heat exchanger fluid therethrough from an intake pipe to an outlet. Each of these tubes are formed from a pair of plates having a solid divider rib going down the center separating the tubes into discrete side flow passages, generally referenced as the liquid side and the vapor side. The flow passages have indented rib patterns therein to vary the flow path through the tubes to enhance the heat exchanger efficiency. The side flow passages are generally interconnected at the bottom end of the tube by a crossover passage which has specialized refrigeration fluid director ribs, as will be further explained.
More particularly, this invention prevents dry out from happening with a specialized rib pattern in the crossover passage which directs refrigerant flow to the region where liquid refrigerant starvation would normally occur. This variation is used on only one side of the evaporator plate because an identical plate is used as the other half of the refrigerant flow tube by interfacing and joining a pair of plates together. Accordingly, the ribs on the overlapping plate have a specialized pattern of ribs designed to distribute and direct liquid refrigerant to the corners of the crossover passage of these tubes. As indicated above, only one set of tooling is required since both halves of the evaporator tubes are identical.
This rib arrangement can be tailored to match any type of rib pattern prevalent in the rest of the tube. The flow distributing and directing ribs are preferably staggered oblong bumps. However, these could be of other suitable shape such as parallel ribs, oval bumps or round bumps. etc.
In view of the above, this invention provides a new and improved evaporator tube which features unique construction that eliminates or sharply reduces local dry out areas in an U-flow evaporator tubing by improving control of the change in phase from a liquid to a gas as the heat exchanger fluid courses through the heat exchanger tubing from the inlet side to the outlet side thereof. More particularly, by feeding increased quantities of heat exchanger liquid or by feeding a mixture containing higher quantity of liquid than vapor to the flow corners of the crossover passage of each tube, dry out areas otherwise normally occurring will be significantly reduced and heat transfer efficiency will be improved.
Accordingly, it is a feature, object and advantage of this invention to provide a new and improved tube for use in a heat exchanger core in which heat exchanger fluid flow paths are provided from the heat exchanger inlet of the tubes to the outlet thereof so that increased quantities of volatile liquid can be fed to the flow corners of the tube so as to be available for vaporization in otherwise dry out areas to thereby increase the heat transfer efficiency of the heat exchanger tubing.
In a preferred embodiment of the present invention, dry out can be effectively eliminated by providing a highly specialized flow directing rib pattern in an interconnecting crossover passage which enhances heat exchanger fluid flow between discrete side flow sections of the tubing. These patterns are arranged to keep the lower part, or corner parts, of each tube adequately fed with liquid heat exchanger fluid so that all portions of the tubing are effectively used to absorb the heat energy of the air blowing past the tubes to change the phase of the heat exchanger fluid from liquid into gas.
The tube pass of this invention provides a highly efficient heat transfer design by providing a first tube section with a plurality of extending rows of ribs side-by-side in first and second side passages or zones to provide a tortuous fluid flow path for high efficiency heat transfer operation. This tube pass further provides a crossover zone interconnecting the first and passages second zones located at the end of the tube pass with an overlapping rib configuration which is angled to direct sufficient liquid from the first zone throughout the crossover zone so that the heat absorption and efficiency is enhanced and dry out areas are reduced or eliminated therein. Moreover, this arrangement provides excellent fluid distribution across the width of the tube pass and within the tube for efficient use of the extensive heat transfer area thus provided.
Further advantages, features and objects of the present invention will become more apparent from the following description and drawings in which: